This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Streptococcus pneumoniae is described as one of the most important pathogens currently plaguing humans, being able to cause several lethal infections including pneumonia and meningitis, while Clostridium perfringens is the third most frequent cause of gastroenteritis and the second most frequent cause of death from foodborne infection. A unifying feature of the virulence mechanisms of these two Gram-positive pathogens is their reliance on an arsenal of extracellular, cell-surface attached glycan degrading enzymes (glycoside hydrolases) that destroy sugars in host tissue. A striking feature of these enzymes is their multi-modularity;they have modules predicted to be dedicated to catalysis, carbohydrate-binding, protein-protein interactions and bacterial cell-wall attachment. Their large size and extent of modularity is extraordinary, with some enzymes containing up to 12 distinct modules. In order to help understand the role of carbohydrate-active enzymes produced by bacterial pathogens, this project will focus on the structure and function of the modular extracellular glycoside hydrolase enzymes secreted by these disease causing bacteria.